Coatings are effective for improving the performance of various materials, such as for achieving better wear resistance and corrosion resistance. Common applications where a coating is applied to a substrate to improve wear resistance of the substrate material include cutting tool inserts for the cutting of hard materials, such as steel. Common substrate materials for cutting tools may include, for example, hard metals of different particle sizes with a varied percentage of cobalt or nickel as a binder material.
Boron nitride (BN) is a well-known material that, due to its thermal and chemical stability, is widely used in the fabrication of parts for high-temperature applications. It exists amorphously and in several crystalline forms. Cubic boron nitride (cBN) is a crystalline form that, due to its very high hardness value and relatively low cost, is widely used in various cutting applications as an abrasive. Since it is relatively insoluble in iron, nickel, and related alloys at high temperature, it is widely used in place of diamond for the cutting and machining of steel.
The art also includes various methods of coating parts, such as inserts for cutting tools and machines, with layers of cBN. The process used has been the application of cBN in pure, non-composite phase. This application of a pure cBN layer by vapor depositions is made with a coating thickness limited to less than about 2 to 3 microns. It has been found, however, that such a coating configuration has limitations for delivering multiple-functional requirements such as toughness, thermal stability, and wear resistance. These parameters are of critical importance in certain applications, such as in coatings for cutting tool inserts, and for this reason an improved coating material is with better toughness, thermal stability, and wear resistance is desired.